KMnO4/Oxalic Acid Titration — Formula Sheet — Notes | NoteTube

$5C_2O_4^{2-} + 2MnO_4^{-} + 16H^+ \rightarrow 10CO_2 + 2Mn^{2+} + 8H_2O$

$Mn^{+7} \xrightarrow{+5e^-} Mn^{+2} \quad \text{(reduction, each KMnO}_4\text{ gains 5e}^-\text{)}$

$C_2O_4^{2-}: C \text{ is } +3 \xrightarrow{-2e^-} CO_2: C \text{ is } +4 \quad \text{(oxidation, each oxalate loses 2e}^-\text{)}$

$n\text{-factor of KMnO}_4 = 5 \quad (Mn: +7 \to +2)$

$n\text{-factor of H_2C_2O_4} = 2 \quad (C: +3 \to +4, \text{ two C atoms each lose 1e}^-)$

$\text{meq of KMnO}_4 = \text{meq of } H_2C_2O_4$

$M_{KMnO_4} \times 5 \times V_{KMnO_4} = M_{H_2C_2O_4} \times 2 \times V_{H_2C_2O_4}$

Parameter	Value	Reason
Temperature	60–70 °C	Reaction too slow at RT; above 70 °C causes decomposition
Indicator	None (self-indicating)	KMnO4 (purple) decolorizes; endpoint = first persistent pink
Medium	Dilute H2SO4	Acidic medium required for Mn7+ → Mn2+
HCl avoided	Yes	HCl reduces KMnO4 (Cl- is oxidized), giving erroneous results

Oxalic acid: OC(=O)C(=O)O KMnO4: [O-][Mn](=O)(=O)=O.[K+] (simplified representation)